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Tertiary Phosphine Induced Migratory Carbonyl Insertion in Cyclopentadienyl Complexes of Iron

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Tertiary Phosphine Induced Migratory Carbonyl Insertion in Cyclopentadienyl Complexes of Iron TERTIARY PHOSPHINE INDUCED MIGRATORY CARBONYL INSERTION IN CYCLOPENTADIENYL COMPLEXES OF IRON by NTAOLENG MAUREEN MAKUNYA DISSERTATION submitted in the fulfilment of the requirements for the degree MASTER OF SCIENCE in CHEMISTRY in the FACULTY OF SCIENCE at the RAND AFRIKAANS UNIVERSITY SUPERVISOR: PROF A. ROODT JUNE 2004 ACKNOWLEDGEMENTS I wish to express my sincere appreciation to Professor A. Roodt for introducing me into this field and for helping all the way through this venture unwearyingly. His dedicated group for their support, it did not go unnoticed. Every thing was made possible by the kind assistance of Mr I. Foster, A. Muller, Dr. L. den Drijver, Dr. W. van Zyl, Dr. M. Haumann, Mrs Y. P. van Sittert, Mrs L. Rossouw, Mr. S. Mokhele and all my friends. I would also like to thank my family for their support all the way. TABLE OF CONTENTS ABBREVIATIONS V ABSTRACT 1 1 INTRODUCTION 3 1.1. GENERAL 3 1.2. IRON AS A CATALYST 6 1.3. AIMS OF PROJECT 8 2 THE ROLE OF ORGANOMETALLIC CHEMISTRY IN CATALYSIS 10 2.1. INTRODUCTION 10 2.2. OVERVIEW OF IRON CHEMISTRY 10 2.2.1. Co-ordination in Organoiron Complexes 11 2.2.1.1. Iron Carbonyl Compounds 11 2.2.1.2. Carbido-clusters 13 2.2.2. Ferrocene and its Derivatives 15 2.2.3. Co-ordination in Bioinorganic Complexes 18 2.2.3.1. Iron Porphyrin Proteins 18 2.2.3.2. Non-Heme Iron Proteins 19 2.2.3.3. Superoxo Reductase 20 2.3. THE ROLE OF CATALYSIS 20 2.4. ACTIVATION OF MOLECULES 22 2.4.1. Ligand Co-ordination and Dissociation 23 2.4.1.1. Steric and Electronic Influences of Ligands on the Process 23 2.4.2. Oxidative Addition 25 2.4.2.1. Concerted Addition 27 2.4.2.2. SN2 Reactions 28 2.4.2.3. Radical Mechanism 29 2.4.2.4. Ionic Mechanism 30 2.5. PROXIMITY INTERACTION 30 2.5.1. Migratory Insertion Reaction 30 2.5.2. Mechanism and Rate Law of the Reaction 33 2.5.3. Factors Affecting Migratory Insertion 37 2.5.3.1. Ligand Effects 37 2.5.3.1.1. Steric Effects 37 2.5.3.1.2. Electronic Effects 38 2.5.3.2. Nature of the Metal 41 2.5.3.3. Lewis Acid 41 2.5.4. Reductive Elimination 42 2.6. APPLICATION IN CATALYSIS 43 2.6.1. Hydroformylation 43 2.6.2. Monsanto Process 46 2.6.2.1. Monsanto Technology 46 2.6.2.2. Function of the Iodide Salt 48 2.6.2.3. BP Low-water Technology (Cativa Process) 48 3 SYNTHESIS AND CHARACTERIZATION OF IRON COMPLEXES 50 3.1. INTRODUCTION 50 3.2. SYNTHESIS AND SPECTROSCOPIC CHARACTERIZATION OF THE COMPLEXES 50 3.2.1. General Considerations 50 5 3.2.2. Synthesis of [(η -C5H5Fe(CO)2)2)], [1] 51 5 3.2.3. Synthesis of [(η -C5H5)Fe(CO)2Me], [2] 53 5 3.2.4. Synthesis of [(η -C5H5)Fe(CO)(COMe){PPh3}] 54 5 3.2.5. Synthesis of [(η -C5H5)Fe(CO)(COMe){P(p-MePh)3}], A 56 5 3.2.6. Synthesis of [(η -C5H5)Fe(CO)(COMe){P(p-FPh)3}], B 56 5 3.2.7. Synthesis of [(η -C5H5)Fe(CO)(COMe){PPhCy2}] 57 5 3.2.8. Synthesis of [(η -C5H5)Fe(CO)(COMe){P(p-MeOPh)3}] 58 3.3. CHARACTERIZATION OF SELECTED COMPLEXES BY X-RAY CRYSTALLOGRAPHY 58 3.3.1. Theoretical Aspects 59 3.3.1.1. Basic Concepts in Crystallography 59 II 3.3.1.2. Structure Factor Fhkl 61 3.3.1.3. Fourier Synthesis 63 3.3.1.4. Patterson Maps 63 3.3.1.5. Least Squares Refinement 64 3.3.1.6. Difference Synthesis 65 5 3.3.2. Structure Determination of [(η -C5H5)Fe(CO)(COMe){P(p- 5 MePh)3}], A, and [(η -C5H5)Fe(CO)(COMe){P(p-FPh)3}], B. 66 3.3.2.1. General 66 3.3.2.2. Data Collection 66 3.3.2.3. Results of Refinement 67 5 3.3.2.4. The Crystal Structure of [(η -C5H5)Fe(CO)(COMe){P(p- 5 MePh)3}], Acetyl(carbonyl)(η -cyclopentadienyl)tri(p-tolylphosphine)- iron(II) 69 5 3.3.2.5. The Crystal Structure of [(η -C5H5)Fe(CO)(COMe){P(p-FPh)3}], Acetyl(carbonyl)(η5-cyclopentadienyl)tri(p-fluorophenylphosphine)- iron(II) 72 3.3.3. Structural Correlations 77 3.3.3.1. Correlation Between Structure of A versus B 77 3.3.3.2. Correlation with Literature Results 80 3.4. CORRELATION OF STRUCTURAL DATA WITH SPECTROSCOPIC FINDINGS 83 4 KINETICS AND MECHANISM OF THE MIGRATORY CARBONYL 5 INSERTION IN [(η -C5H5)Fe(CO)2Me] 86 4.1. INTRODUCTION 86 4.2. RATE LAWS AND REACTION ORDERS 87 4.3. ACTIVATION PARAMETERS 89 4.4. EXPERIMENTAL PROCEDURE 91 4.4.1. General Data 91 4.4.2. Kinetic and Spectroscopic Studies 92 4.5. MECHANISTIC ASPECTS AND RATE LAW 95 4.5.1. Basic Arguments for Mechanistic Scheme and Rate Law 95 4.5.2. Results and Discussion 100 III 4.5.2.1. Insertion Induced by Tri-p-tolylphosphine P(p-MePh)3 101 4.5.2.2. Insertion Induced by Tri-p-fluorophenylphosphine P(p-FPh)3 106 4.5.2.3. Insertion Induced by Triphenylphosphine PPh3 119 4.6. CORRELATION OF DATA FOR PX3 (X = (p-FPh) and (p-MePh)) 120 4.7. RATE LAW FOR THE PROPOSED REACTION SCHEME 121 4.7.1. Possible Schemes for the Reaction 121 4.7.2. Formation of an Outer-sphere Intermediate Species (Scheme 4-1) 122 4.7.3. Formation of an Acyl Intermediate Species (Scheme 4-2) 124 4.7.4. Proposed Final Mechanism and Rate Law 126 4.7.5. Conclusion 127 5 EVALUATION OF RESULTS AND FUTURE RESEACH 128 5.1. SCIENTIFIC EVALUATION OF THIS STUDY 128 5.2. FUTURE RESEARCH 130 APPENDIX 132 5 A.1. CRYSTAL DATA OF [(η -C5H5)Fe(CO)(COMe){P(p-MePh)3}] 132 5 A.2. CRYSTAL DATA OF [(η -C5H5)Fe(CO)(COMe)P(p-FPh)3] 135 A.3. CALCULATION OF THE EFFECTIVE CONE ANGLE 138 A.4. EQUATIONS OF LEAST-SQUARES PLANES IN COMPLEX A AND B142 A.5. DERIVATION OF THE RATE LAWS 143 A.5.1. Formation of the Outer-sphere Intermediate Species 143 A.5.2. Formation of the Acyl Intermediate Species 146 A.6. SUMMARY OF METHODS USED TO DRY SOLVENTS 148 A.6.1. Dichloromethane 148 A.6.2. Acetonitrile 148 A.7. SUPPLEMENTARY DATA FOR P(p-MePh)3 149 A.8. SUPPLEMENTARY DATA FOR P(p-FPh)3 151 A.9. SPECTROSCOPY DATA 156 IV ABBREVIATIONS AO = Acid optimisation Alumina = Aluminium oxide Ph = Phenyl Cp = Cyclopentadienyl DCP = Dicyclopentadiene FT-IR = Fourier-transform infrared IR = Infrared kobs = Observed pseudo first order rate constant L = Ligand [L] = Concentration of the ligand Me = Methyl group NMR = Nuclear magnetic resonance Cy = cyclohexyl PX3 = tertiary phosphine QALE = quantitative analysis of ligand effect Tbp = Trigonal bipyramidal THF = Tetrahydrofuran UV-visible = Ultra violet-visible ABSTRACT The aim of this study was to investigate the mechanism of phosphine induced migratory carbonyl insertion in the monocyclopentadienyliron(II) carbonyl complex, [η5- (C5H5)Fe(CO)2Me], upon variation of different parameters such as the type and the concentration of the phosphine ligand and the solvent. The mechanism that agrees with the results obtained is presented below. 5 Characterization of the products of the reaction, [η -(C5H5)Fe(COMe)(CO){P(p-MePh)3}], A, 5 and [η -(C5H5)Fe(COMe)(CO){P(p-FPh)3}], B by X-ray crystallography, shows that both the complexes crystallize in the triclinic crystal system and space group P1 with R = 4.0 and 4.3 % for A and B respectively. The Fe-P and M-(C≡O) bond distances, which should be sensitive to the electron density around the metal centre are the same within the estimated standard deviation [(M-PA = 2.193(8) and M-PB = 2.194(8) Å while M-(C≡O) = 1.746(3) and 1.748(3) Å for both A and B respectively]. The effective cone angle of P(p-MePh)3 in A is 152.6 ˚ and for P(p-FPh)3 in B 152.4 ˚. This is larger than the classic Tolman cone angle in literature, ustilising Ni-P values of 2.28 Å, since the Fe-P bond distances are shorter. The variation in the angle P-Fe-Centroid angles are 126.1(1) ˚ and 127.4(1) ˚ for A and B respectively. The dihedral angles between plane 1 (plane described by Cp ring) and plane 2 [plane described by P, C(1) and C(2)] is 6.9(2) ˚ for A and 8.1(2) ˚ for B. 5 [η -(C5H5)Fe(CO)2Me] undergoes migratory carbonyl insertion in the presence of the PX3 ligands [X = (p-MePh) and (p-FPh)]. Two distinct reactions, as depicted by the Scheme below, were observed in MeCN for P(p-FPh)3, but not for P(p-MePh)3. ABSTRACT K1, k1 [(η5−C5H5)Fe(CO)2(Me)] + PX3 [(η5−C5H5)Fe(CO)2(Me), PX3]# k-1 k2 5 [(η −C5H5)Fe(COMe)(CO){PX3}] Due to the fact that the reactions were very slow, the quality of the data, as well as the reproducibility thereof, was not that good and very large variations in rates have been obtained for some kinetic runs. However, the data could still be used to derive a reasonable mechanism for the overall reaction.
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